The government's controversial child benefit reforms came into force today and look set to affect around one million families earning over £50,000 a year.

Most will lose some - or all - of their child benefit payments, as the UK coalition government seeks to claw back £1.5bn a year to help pay down the public deficit.

While over 250,000 higher earners have already voluntarily opted out of the system, hundreds of thousands more will continue to receive the benefit - worth around £1,300 a year to the average family - but will have to repay it through their taxes. They will also be forced to fill in a series of self-assessment forms.

The new rules mean that families with one parent earning over £60,000 a year will lose the right to the benefit, currently £20.30 a week for the first child and £13.40 a week for each subsequent child.

Families where one parent pulls in between £50,000 and £60,000, will see the benefit reduced on a sliding scale.

But in a bizarre anomaly, double income families where both parents earn up to £49,000 - just below the £50,000 threshold - will be able to keep their benefit, while households with one parent on £60,000 and the other not working will lose all theirs.

Just last week, HMRC admitted that it failed to contact around 300,000 families about imminent changes to child benefit payments that could see them lose the valuable subsidy.

The taxman had previously said that it would contact 1.1m people to alert them to the fact they will lose the right to claim child benefit from January 7, when it will be means-tested.